A number of power divider/combiner configurations have been developed to divide a microwave input signal into a number of signals to feed multiple solid state devices such as power transistors, and to combine the output signals from these devices into a single signal. The term microwave as used herein is intended to include both microwave and millimeter wave signals.
Several different geometries have evolved to accomplish these divider/combiner functions, including circular, radial and planar configurations. Examples of these configurations are disclosed in E. J. Wilkinson, "An N-way Hybrid Power Divider," IRE Trans. on Microwave Theory and Tech., vol. MTT-8, pp. 116-118, Jan. 1960; in U.S. Pat. No. 4,234,854, entitled "Amplifier With Radial Line Divider/Combiner", issued Nov. 18, 1980, to Schellenberg et al.; N. Nagai, E. Maekawa and K. Ono, "New N-Way Hybrid Power Dividers," IEEE Trans. on Microwave Theory and Tech., vol. MTT-25, pp. 1008-1012, Dec. 1977; and U.S. Pat. No. 4,835,496, entitled "Power Divider/Combiner Circuit", issued May 30, 1989, to Schellenberg et al.
One particular application for a microwave divider-combiner is to connect together multiple power transistor chips to form a high power amplifier. These chips may take the form of GaAs Metal Field Effect transistors (MESFETSs) or bipolar transistors. Power amplifiers of this type may be packaged as hybrid circuits in metal-ceramic hermetically sealed packages. Such elements, particularly the transmission lines, also referred to as matching networks, which act as signal paths between the multiple chips and the single input-output ports. A requirement for these transmission lines is that they provide equi-distant and symmetric signal path lengths between the transistor chip terminals and the input/output ports in order to provide equiphase combining-dividing functions. Further, it is desirable to maintain the width of the various signal paths at less than half a wavelength in order to minimize parasitic resonances.
In order to minimize the package size and amplifier power requirements, it is desirable to use the minimum number of transistor chips needed to provide the desired output power level. Often, this will result in the need to use an odd number of multiple transistor chips.
Accordingly, it is an object of the invention to provide a compact divider/combiner circuit which meets the above criteria and is suitable for use in providing the desired signal paths from an odd number of multiple transistor chips housed in a hybrid circuit package.